There have been proposed devices for detecting pressure abnormalities in a hydraulic system having a mechanism that properly adjusts the pressure of engine oil in accordance with the operating state of an internal combustion engine.
Japanese Laid-Open Patent Publication No. 11-270323 discloses a device that detects abnormalities of a hydraulic system based on a comparison between the actual oil pressure and a lowest oil pressure that corresponds to the engine speed and the coolant temperature. This device determines that there is an abnormality when the actual oil pressure is lower than the lowest temperature, and outputs a warning signal.
Japanese Laid-Open Patent Publication No. 6-101439 discloses that an abnormality in a regulator valve for switching oil pressure is detected based on time for switching the regulator valve.
Japanese Laid-Open Patent Publication No. 2005-188434 discloses a device that detects abnormalities of a hydraulic system based on a comparison between the actual oil pressure and a lowest oil pressure that corresponds to the engine speed and the engine oil temperature. This device determines that there is an abnormality when the actual oil pressure is lower than the lowest temperature, and outputs a warning signal.
The devices disclosed in the above described Japanese Laid-Open Patent Publication Nos. 11-270323 and 2005-188434 cannot detect abnormalities in switching operations of oil pressure adjusting mechanisms such as regulator valves. Since the device disclosed in Japanese Laid-Open Patent Publication No. 6-101439 determines an abnormality directly based on the operating time of the regulator valve, the device is capable of detecting abnormalities in the operation of the regulator valve. However, this device cannot detect abnormalities in parts in the hydraulic system other than the regulator valve.